The present invention relates to the preparation of saturated aliphatic dicarboxylic acid bis-N-chloramides.
N-chloramides of monocarboxylic acids are easily, and with a high yield, accessible through the chlorination of appropriate monocarboxylic acid amines. However, if these processes known for monoamides are applied to aliphatic dicarboxylic acid diamides, one generally obtains the desired bis-N-chloramides only with a low yield. Only pursuant to a process described in German Pat. No. 909 455, which was especially developed for the preparation of bis-N-chloramides, it is possible to obtain higher yields in the case of pimelic acid diamide and adipic acid diamide, if chlorination is carried out either in aqueous-alkaline media, in glacial acetic acid or other organic acids with addition of alkali salts or salts of the alkaline earth metals of these acids or also in other solvents, whereby, however, a hydrogen halide must always be added as acceptor.
Conversion in an alkaline medium is disadvantageous for several reasons. The obtainable products are non-uniform, they contain unreacted diamide, furthermore dicarboxylic acid formed through hydrolysis of the diamide and the bis-N-chloramide, as well as bis-N-dichloramides formed through perchlorination of the bis-N-chloramide. Bis-N-dichloramides are also formed during chlorination in organic acids or other organic solvents in the presence of hydrogen halide acceptors. They decompose during boiling, thereby forming extremely explosive decomposition products (Rayon plus Synthetic plus Rayon Staple, 29, page 43 (1951) and thus considerably endanger the execution of this known process.
According to another version described in German Pat. No. 909 455, bis-N-chloramides are allegedly obtainable with almost quantitative yield if the dicarboxylic acid diamide is admixed in the dry state with an agent that will bond hydrogen halide, preferably sodium bicarbonate, and chlorine vapors are conducted over the dry mixture. However, these methods as well are not suitable for the industrial-scale preparation of bis-N-chloramides: the reaction mix cakes during dry chlorination, it has to be continuously detached from the reactor walls and remixed. In addition, the continuous taking of samples is necessary, in order to determine the degree of chlorination, so that the supply of chlorine can be interrupted at the correct time. The process is also problematical because of corrosion.
The conversion of tere- and isophthalic acid diamides to the corresponding bis-N-chloramides through chlorination in an aqueous medium of mineral acids if known from German Patent Disclosure No. 2 313 548. The application of this process known for the two above-mentioned aromatic dicarboxylic acid amides was not obvious to the extent that the expert had to conclude from the statements in Rayon plus Synthetic plus Rayon Staple, that, in the presence of excess hydrochloric acid, the aliphatic N-chloramides would again dissociate into amides and chlorine (loc. cit., page 8 at the bottom).